🔩 Drill Bit Size Chart
Complete reference table for number (#80–#1), letter (A–Z), and fraction drill bits. Includes decimal inch and metric equivalents. Click any column header to sort.
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| Drill Size | Fraction | Decimal (in) | Metric (mm) |
|---|---|---|---|
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Number Drills
Number drills range from #80 (0.0135") — the smallest — up to #1 (0.228"). Higher numbers = smaller diameters. Commonly used for pilot holes, rivet holes, and tapping operations. #30 (0.1285") and #40 (0.098") are among the most common in airframe sheet metal work.
Letter Drills
Letter drills run from A (0.234") to Z (0.413"), picking up where number drills leave off. Letter drills are common for larger bolt clearance holes. Drill E (0.250") = exactly 1/4 inch. U = 3/8".
Fraction Drills
Fraction drills are specified in 64ths of an inch (1/64 through 1/2" and beyond). Used when a precise fractional hole diameter is required. Common in structural repair and hardware installation. Always verify the drill size against the AMM or SRM.